The alloy indium gallium nitride (InxGa1-xN) is part of the family of III-nitride materials, including for example, gallium nitride (GaN), aluminum nitride (AlN), indium nitride (InN) and alloys thereof. InGaN alloys can be used in an array of device structures, including, for example, electronic, optoelectronic, photovoltaic and microelectromechanical systems.
Layers of InGaN can include undesirable pits, which are commonly V-shaped. The pits generally develop at locations at which a defect, such as a threading dislocation, intercepts a GaN/InGaN interface. The V-shaped pits typically grow in size dependent on the thickness of the InGaN layer and can extend through the entire thickness of the InGaN layer. For example, a V-shaped pit can extend through the entire active region of a light-emitting device, such as a light-emitting diode or laser diode. In some instances, the light-emitting device may be rendered inoperable because a V-shaped pit allows the electrical contacts of a device structure to short circuit one another. Hence, it is desirable to form indium gallium nitride layers that have fewer pits.
As discussed in more detail in Applied Physics Letters 90, 191908 2007, Keller et al. noted a reduction in the size of V-shaped pits when N-polar InGaN layers are formed on N-polar GaN layers. Further, Keller et al. found that a higher percentage of indium atoms can be incorporated with N-polar InGaN layers for a given set of growth parameters, for example, for a given growth temperature.
However, Keller et al. formed N-polar gallium nitride layers by direct growth on a growth substrate (e.g., a sapphire substrate). Such direct growth of N-polar GaN films can involve complex processes, which may produce highly dislocated GaN material with undesirable surface roughness. The growth of N-polar InGaN layers on such poor quality highly dislocated GaN material may in turn also be highly dislocated and therefore can be less attractive for use in state of the art semiconductor devices.